NiFe2O4 Phase Research Articles

Investigation of structural and magnetic properties of Ni, NiFe and NiFe2O4 thin films

Soft magnetic thin films of Ni, NiFe and NiFe2O4 were prepared using reactive magnetron sputtering in various deposition conditions. Experimentally observed soft magnetic property was compared and correlated with nanocrystalline structure evolution. Ni and NiFe deposited films are textured with fcc(111) phase preferred orientation. Accordingly, grain size and lattice parameter were calculated from X-ray diffraction (111) peak line width and 2θ peak position. Addition of reactive gas oxygen in deposition process has substantial effect on crystalline structure of film. There is phase transition from the ordered NiFe (111) structure to the NiFe2O4 nanocrystalline phase. The resulting film has shown small X-ray diffraction intensity peak corresponding to (311) and (400) orientation, indicating small amount of existing NiFe2O4 phase. The mechanism has been discussed to be responsible for nanocrystallization and amorphization of NiFe2O4 films. Magnetic measurement (M-H) loop reveal soft magnetic nature of films with magnetic anisotropy. The coercivity (Hc) of films is in accordance with random anisotropy model, where Hc reduced with grain size. The structural transformation was supported by Fourier transforms infrared spectroscopy measurement. The films are highly smooth with surface roughness in the range of ∼0.53–0.93nm. NiFe2O4 films have shown lowest surface roughness with highest electrical resistivity values. The structural, surface, magnetic and infrared spectroscopy results are observed and analyzed.

Mechanochemically activated synthesis of nanostructured NiFe2O4

Powdery NiFe2O4 has been obtained by mechanothermal treatment. Nickel and iron hydroxides are used as initial compounds. For comparison the initial compounds are calcinated without mechanical treatment (samples obtained by direct heating). The characterization of the samples is carried out by XRD analysis and Mossbauer spectroscopy. It is established that single phase NiFe2O4 is formed after mechanical activation (5 h) and calcination at 773 K. The ferrite synthesized at this temperature contains a smaller quantity of Fe3+ ions in tetrahedral position (31%) than is the case of conventional nickel ferrite (50%). The number of tetrahedrally coordinated iron ions increases with enhancement of the synthesis temperature, approaching the distribution of the tetrahedral and octahedral positions typical of conventional NiFe2O4. The samples obtained by direct heating contain unreacted NiO and α-Fe2O3 even after calcinations at 1073 K.

Catalytic properties of cobalt and nickel ferrites dispersed in mesoporous silicon oxide for ethylbenzene dehydrogenation with CO2

A polymeric precursor method was applied to synthesize catalysts of the general formula MFe2O4 (M = Co and Ni) in order to contribute to studies on ethylbenzene dehydrogenation in the presence of CO2. The catalysts were characterized by TG, H2-TPR, XRD, Mossbauer spectroscopy (MS), N2 adsorption/desorption isotherms and TPD-CO2. Investigations using XRD and MS revealed that the spinel structures of CoFe2O4 and NiFe2O4 phases were formed. The catalytic results suggested that materials with a spinel structure are particularly interesting for ethylbenzene dehydrogenation. Compared to the other catalysts synthesized the sample containing cobalt ferrite showed higher conversion and good styrene selectivity. The analysis of the spent catalyst (DRX) showed that the CoFe2O4 phase was stable under the reaction conditions and that a coke (TG) deposit was more pronounced for the NiFeSi.

Magnetoelectric coupling in NiFe2 O4-BiFeO3 composite films

Multiferroic xNFO-(1-x)BFO (x =0.00 0.10, 0.15, 0.20, 0.25) composite films are prepared through self-assembling growth on Au/Ti/SiO2/Si substrates by chemical solution deposition (CSD). X-ray diffraction analysis shows that the perovskite BiFeO3 and the spinel structured NiFe2O4 phases are formed and separated. The leakage current density (J) in the film decreases and the remnant polarizations (M r) increases with the introduction of NFO. The value of J in 0.25NFO—0.75BFO film is found to be nearly two orders of magnitude lower than that in the BFO film, and the M r and the saturation magnetization ( M s) reach maxima, i.e. 2.3μC/cm2 and 70.2 kA·m-1, respectively. Therefore, from the calculation for magnetic moment of NFO we can conjecture that magnetoelectric coupling exists in the composite films.

Structural and Raman characterization of nanogranular BaTiO3‐NiFe2O4 thin films deposited by laser ablation on Si/Pt substrates

AbstractThin films composed by (BaTiO3)1‐x‐(NiFe2O4)x with different nickel ferrite concentrations (x) have been deposited by pulsed laser ablation on platinum covered Si(001) substrates. The films structure was studied by X‐ray diffraction and Raman spectroscopy. It was found that the NiFe2O4 phase unit cell was expanded along the growth direction of the films, with a lattice parameter that increased with increasing NiFe2O4 concentration. The opposite behavior was observed on the BaTiO3 phase, with an expansion of its unit cell that lowered with increasing x. The presence of the strain in the films induced a redshift of the Raman peaks of NiFe2O4 that decreased with increasing NiFe2O4 concentration. Cation disorder in the nickel ferrite was observed for lower x, where the nanograins are more isolated and subjected to more strain, which was progressively decreased for higher NiFe2O4 content in the films. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Exchange-biased NiFe2O4/NiO nanocomposites derived from NiFe-layered double hydroxides as a single precursor

NiFe2O4 nanoparticles (<10 nm) embedded in a NiO matrix have been fabricated by calcining the corresponding NiIIFeIII-layered double hydroxide (LDH) precursors at high temperature (500 °C). Compared with the NiFe2O4/NiO nanocomposite obtained by calcination of a precursor prepared by a traditional chemical coprecipitation method, those derived from NiFe-LDH precursors show much higher blocking temperatures (T B) (˜380 K). The enhanced magnetic stability can be ascribed to the much stronger interfacial interaction between NiFe2O4 and NiO phases due to the topotactic nature of the transformation of the LDH precursor to the NiFe2O4/NiO composite material. Through tuning the NiII/FeIII molar ratio of the NiFe-LDH precursor, the NiFe2O4 concentration can be precisely controlled, and the T B value as well as the magnetic properties of the final material can also be regulated. This work represents a successful example of the fabrication of ferro(ferri)magnetic (FM)/antiferrimagnetic (AFM) systems with high magnetic stability from LDH precursors. This method is general and may be readily extended to other FM/AFM systems due to the wide range of available LDH precursors.

An attempt to produce NiFe2O4 powder from electrodeposited Fe–Ni alloy powders by subsequent recrystallization in air

The electrodeposition of the Fe–Ni powders from citrate-ammonium chloride containing electrolytes for different Ni/Fe ions concentration ratios at pH 4.0 was investigated by the polarization measurements. The morphology, chemical composition, and phase composition of the obtained powders were investigated using SEM, EDS, and XRD analysis. EDS analysis of as-deposited alloy powders confirmed anomalous co-deposition of Fe and Ni. A common characteristic for all as-deposited powder samples was the presence of cone-shaped cavities and nodules on the big agglomerates of the order of 200–400 μm. After annealing in air at 400, 600, and 700 °C for 3 h, all alloy powders oxidized forming NiO, NiFe2O4, and Fe2O3 phases in different proportions depending on the original powder composition. The NiFe2O4 phase was found to be dominant in the sample with the highest percentage of Fe after annealing at 600 °C.

Thermal Annealing Effects on the Structural, Magnetic, and Magnetotransport Properties of NiFe/(Ni,Fe)O Bilayers

In this study, the exchange bias and magnetoresistance of NiFe/(Ni,Fe)O bilayers were investigated. Transmission electron microscopy has shown that the (Ni,Fe)O single layer is a pure rock-salt solid solution (a= 4.24 Å). After annealing at 500 °C for 2 h, the (Ni,Fe)O film undergoes a phase transformation from the pure antiferromagnetic (Ni,Fe)O into ferromagnetic Ni (a= 3.53 Å) and ferrimagnetic NiFe2O4 (a= 8.29 Å) phases. Furthermore, the NiFe/as-deposited (Ni,Fe)O bilayers exhibit a strong temperature dependence of exchange bias field [Hex(T)] that increases linearly with decreasing temperature (Hex= -30 Oe at 150 K). Surprisingly, no Hex was observed in the NiFe/annealed (Ni,Fe)O bilayers, even at 150 K. This indicates that the AF (Ni,Fe)O phase provides stronger exchange coupling than the ferrimagnetic NiFe2O4. Magnetotransport measurements have shown that these NiFe/(Ni,Fe)O bilayers exhibit anisotropic magnetoresistance (AMR). The NiFe/as-deposited (Ni,Fe)O bilayers exhibit a higher MR ratio than the NiFe/annealed (Ni,Fe)O bilayers, which suggests stronger anisotropic electron scattering between the NiFe and (Ni,Fe)O interfaces in the annealed system.

Investigation of magnetic behaviour of Ni–Fe–O prepared by the solid state method

Polycrystalline Fe doped NiO was prepared by the solid state method with the aim of exploring its suitability as a functional material for spintronics applications. Phase pure samples (up to 2% doping of Fe) as evident from x-ray diffraction were characterized to investigate the magnetic, electric and dielectric properties. Magnetic measurements using the vibrating sample magnetometer clearly reveal ferromagnetic behaviour at room temperature. The activation energies of the doped samples, determined from impedance spectroscopy, were found to be relatively higher than that of undoped NiO. It is also observed that Fe doping has no significant effect on the dielectric properties of the samples. Thermogravimetric analysis, carried out to find the Curie temperature (TC), leads to a remarkable insight into the observed ferromagnetism by identifying the presence of secondary phase NiFe2O4.

Catalytic Oxidation of CO Over Synthesized Nickel Ferrite Nanoparticles from Fly Ash

Catalytic oxidation of carbon monoxide (CO) gas over nanosized nickel ferrites prepared from fly ash has been investigated. X-ray diffraction analyses showed that pure crystalline nickel ferrite, NiFe2O4, phase can be obtained by thermal treatment of the precursors at temperature >800 °C for 120 min in the studied pH range, from 7 (neutral) to 12 (highly alkaline). In the temperature range 500 ≤ T ≤ 800 °C, impure low crystalline NiFe2O4 phase formed. The main impurities are FeO (OH) and Fe2O3 · H2O phases. Higher magnetization (32 emu/g) is obtained for a precursor precipitated at pH 10 and thermally treated at 1,200 °C for 120 min. The catalytic oxidation of CO over nanocrystalline NiFe2O4 powders was studied using quadrupole mass gas analyzer system. The main parameters as crystal size, surface area and firing temperature are used to clarify the efficiency of using NiFe2O4 powders in catalytic oxidation of CO. It was found that the efficiency of catalytic oxidation decreased by increasing firing temperature and crystallite size of the samples. The lower crystal size (2–8.5 nm), the higher surface area (25–55 m2/g) and the presence of impurities FeO(OH) phase enhanced CO adsorption and consequently its oxidation.

Exchange bias and the origin of room-temperature ferromagnetism in Fe-doped NiO bulk samples

A series of Ni(1−x)FexO (x=0, 0.015, 0.03, 0.05, and 0.1) bulk samples was synthesized by the chemical concentration-precipitation method. Phase composition analysis was carried out, which showed that trace amounts of ferromagnetic phase NiFe2O4 could not be detected by x-ray diffraction in these bulk samples with x≤0.03. When x&amp;gt;0.03, NiFe2O4 ferrite is detected easily. The magnetic properties of all the bulk samples were investigated by measuring their magnetization as a function of temperature and magnetic field. The results indicated that all the bulk samples sintered in air exhibited large room-temperature ferromagnetic behavior ascribed to a ferromagnetic impurity phase. Simultaneously, an exchange bias and training effect were also observed in all the bulk samples, suggesting the possibility of the existence of a strong ferromagnetic/antiferromagnetic exchange coupling in this kind of compound. Specifically, the exchange bias field could be tuned by changing the concentration of the Fe dopant.

Dielectric and Magnetic Properties of BaTiO&lt;sub&gt;3&lt;/sub&gt;/NiFe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; Composites

A series of ferrroelectric-ferromagnetic composites were synthesized from BaTiO3 and NiFe2O4 ferrite by conventional solid-state route. XRD studies indicated that the composites comprised of only two phases, BaTiO3 phase with perovskite structure and NiFe2O4 phase with spinel structure. Frequency dependence of permittivity and permeability were also measured. Experimental results showed that the dielectric constant and initial permeability of these composites could be tunable by varying the composition of composites. Thus, these composites can be used for multilayer chips EMI filters.

Abrupt Slope Change in Temperature Dependence of Resistivity in Ni-Fe-O Sintered Body

NiFe2O4+ 0∼100 vol.% NiO sintered bodies were prepared by mixing NiFe2O4 and NiO powders, and subsequent sintering at 800°C in air for 1 hour. Slopes in the temperature dependence of resistivity curves in the system have been found to abruptly changed, except for a composition of NiFe2O4+ 50 vol.% NiO. To investigate the mechanism of this phenomenon, NiFe2O4 powder was analyzed by high temperature X-ray diffraction, a thermo-gravimetry and differential thermo analysis. In the range from 100 to 300°C, the structure of NiFe2O4 phase does not change. Therefore the mechanism of this phenomenon is not related to any phase transition or the contamination of NiO.

Synthesis and electrophoretic deposition of magnetic nickel ferrite nanoparticles

Powders with particle size ∼5–15 nm of nickel ferrite have been synthesized chemically from aqueous precursor solutions. From the structural and magnetic properties, it is determined that the synthetic material possesses high NiFe2O4 phase purity and controllable particle size. The optimum calcination temperature is found to be ∼500 °C, at which the NiFe2O4 particles exhibit a saturation magnetization of 2800 G, and a particle size of about 10 nm. The particles are then deposited onto silicon substrates by electrophoretic deposition (EPD) process. The Ni ferrite particles are suspended in a medium of isopropyl alcohol with magnesium nitrate and lanthanum nitrate salts as charging agents. The transportation of particles to the substrate surface is assisted by applied electric field and particles adhere to the substrate surface by a glycerol based surfactant. The magnetic response of the EPD film has been investigated by vibrating sample magnetometer (VSM) measurements.

Direct and alternating current magnetic properties of FeNi particles coated with SiO2

FeNi particles coated with SiO2 have been prepared by a rapid and simple chemical synthesis. The precursor compound has been reduced in hydrogen gas at different temperature and its structure and magnetic properties were studied. The experimental results showed that the Ni3Fe and NiFe2O4 (or Ni1.43Fe1.7O4) phases co-existed when treated at 500°C and only the Ni3Fe phase existed when treated above 600°C. The particles exhibited a dependence of the magnetization on the H2 reduction temperature and the SiO2/FeNi weight ratio. The specific magnetization σS increased and the coercive force HC decreased with increasing reduction temperature. This result can be explained by an incomplete conversion of the precursor compound to Ni3Fe during the reduction procedure. There was a decrease in σS and increase in HC with the increase of SiO2/FeNi ratio. The coated materials have lower permeability than the uncoated materials and the μ′ of the sample 10% SiO2/FeNi is frequency-independent.

In Situ Raman Spectroscopic Investigation of Stainless Steel Hydrothermal Corrosion

Abstract In situ Raman spectroscopy was used to investigate corrosion of Type 304L stainless steel ([SS] UNS S30403) in airsaturated water at a pressure of 25.2 MPa and temperatures up to 496°C in an optically accessible flow cell. The exposed Type 304L SS coupon also was characterized ex situ with Raman spectroscopy and scanning electron microscopy. After exposure, nickel(II) iron(III) oxide (NiFe2O4) and alpha chromium(III) oxide hydroxide (α-CrOOH) phases were detected on the coupon surface. The NiFe2O4 phase was first identified after the coupon was heated to 247°C and was observed under all subsequent conditions. Upon heating from 247°C to 326°C, the crystallinity and possibly the thickness of the NiFe2O4 phase increased. The α-CrOOH phase was first identified after the coupon was heated to 326°C and was observed under all subsequent conditions. At least a portion of the α-CrOOH phase probably originated as a corrosion product released from the optical cell and/or flow system. In situ Raman spectra i...

Preparation of Nickel Ferrite Using Liquid Metal Carboxylates

Unusual metal carboxylates that are liquids at room temperature have been synthesized and applied to the preparation of nickel ferrite. These salts Ni(MEEA)2·0.5H2O and Fe3O(MEEA)7·5.5(H2O) bear the polyether carboxylate anion 2-[2-(2-methoxyethoxy)ethoxy]acetate (MEEA = CH3OCH2CH2OCH2CH2OCH2CO2-). They may be utilized for the low-temperature preparation of nickel ferrite by using Ni(MEEA)2·0.5H2O to coat Fe2O3 powders with a continuous film of NiO. Upon heating this material to 800 °C, a remarkable solid-state reaction occurs to puff the precursor particles into broccoli floret-like collections of very small particles. A homogeneous precursor solution for nickel ferrite may be prepared via dissolution of Ni(NO3)2 in Fe3O(MEEA)7·5.5(H2O). This precursor solution yields a metastable amorphous NiFe2O4 phase at 300 °C which undergoes an exothermic crystallization at 374 °C with an energy change of −126.1 kJ/mol.